Acronym in astronomy: TNO for trans-Neptunian object

Since the deomotion of Pluto to dwarf planet status, Neptune is the outermost planet of our solar system. A body orbiting the sun beyond Neptune's orbit is called a trans-Neptunian object, TNO for short.  For example, Eris, Pluto (!),  2005 FY₉, 2003 EL₆₁, Sedna, Orcus, Quaoar and Varuna are TNOs (shown to scale and in reference to the size of Earth in Figure 4.9 in [1]). Many more are known—classified, numbered, but often without a common name [2,3].

Often, TNOs come in pairs, called binaries:  two bodies with similar masses that orbit each other [4]. Pluto and its moon Charon are such a couple [5].

TNOs are not planets. Three TNOs are called dwarf planets: Pluto, Eris, and Makemake [6]. Ceres also is a dwarf planet, but not a TNO. Ceres belongs to the asteroid belt between Mars and Jupiter.

The use of the prefix trans (typically meaning through) in the term trans-Neptunian has occasionally been critized, since, what really is meant is ultra in the sense of  beyond. However, then we would get the term ultra-Neptunian object and the acronym UNO. The latter stands for United Nations Organization, concerned primarily with one object—our home planet.

Keywords: astronomy, planetary science, solar system, celestial bodies, terminology.

References and more to explore
[1] Neil deGrasse Tyson: The Pluto Files. W. W. Norton & Company, New York and London, 2009; pages 67, 91 and others.
[2] IAU Minor Planet Center > List Of Transneptunian Objects: www.minorplanetcenter.org/iau/lists/TNOs.html.
[3] List of Known Trans-Neptunian Objects: www.johnstonsarchive.net/astro/tnoslist.html.
[4] The Planetary Society > Explore > Space Topics -Trans-Neptunian Objects: http://planetary.org/explore/topics/trans_neptunian_objects/.
[5] 30 Years Since Charon Reveals Pluto To Be A Binary Planet System: http://www.spacedaily.com/reports/Thirty_Years_Since_Plutoid_Revolution_Began_999.html.
[6] IAU > Fourth dwarf planet named Makemake:  http://www.iau.org/public_press/news/detail/iau0806/.